1. Field of the Invention
The present invention relates to a wheel manufacturing method.
2. Description of the Related Art
One-piece type wheels which are integrally molded by casting, two-piece type wheels with a construction that is split into two parts, i.e., a rim and a disk, and three-piece type wheels with a construction that is split into three parts, i.e., an inner rim, and outer rim and a disk, are widely used as vehicle wheels that consist of light alloys such as aluminum alloys or the like.
In the case of two-piece type wheels and three-piece type wheels, wheels in which the disk is manufactured by casting or forging, and the rims are constructed using rolled metal plates have been adapted for practical use. Rims that are used in such cases include products in which band form rolled metal plates are rolled up into a cylindrical shape, both ends are welded, and the produced is molded into a desired shape by spinning, and products in which circular plate form rolled metal plates are press-molded into a cylindrical shape with a bottom, the bottom part is cut away, thus forming a cylindrical molded product that has flange parts, and this product is molded into a desired shape by spinning.
Furthermore, during turning and the like, a large force acts on at least the rim flange part on the design side compared to the rim flange part on the attachment side; accordingly, in order to increase the strength and rigidity of this part, parts that are constructed with an increased thickness, or parts that are folded back or curled into a cylindrical shape have been adapted for practical use (e.g., see Japanese Patent Application Laid-Open No. 2003-236638 and Japanese Patent Application Laid-Open No. 2003-236636).
In the case of one-piece type wheels, the strength can be increased by forming the rim flange parts with an increased thickness at the time of casting; however, in the case of two-piece type wheels and three-piece type wheels, because the rims are molded using rolled metal plates that have a uniform thickness, it is necessary to increase the strength of the rim flange parts by folding back the rim end parts or curling these parts into a cylindrical shape, and when the wheel is plated, the plating liquid accumulates on the inside of the folded-back part or curl, thus causing corrosion to occur in the rim flange parts.
Accordingly, wheel manufacturing methods have been proposed which are devised so that rim flange parts can be molded by increasing the thickness in two-piece type wheels and three-piece type wheels as well (for example, see Japanese Patent Application Laid-Open No. 2-160131). In such manufacturing methods, a circular plate form rolled metal plate is press-molded into a cylindrical shape that has a bottom, and the bottom part is cut away, thus manufacturing a cylindrical molded product that has flange parts. When this is subjected to spinning, a rolling roller is moved from the end part of the substantially cylindrical trunk body part toward the sides of the flange parts while being pressed against these parts so that the metal material on the side of the trunk body part is caused to move toward the sides of the flange parts, thus increasing the thickness of the flange parts; afterward adjusting the shape of the flange parts, and thick rim flange parts can be molded without folding back the rim end parts or curling these parts into a cylindrical shape.